Mechanical, dielectric properties and thermal shock resistance of porous silicon oxynitride ceramics by gas pressure sintering

Porous silicon oxynitride (Si2N2O) ceramics were prepared by gas pressure sintering with 2.5-10.0 mol% Li2O as additive. The influences of Li2O content on phase, microstructure, mechanical and dielectric properties of the Si2N2O ceramics were investigated. XRD analysis showed that the increase of Li2O content facilitate both the densification and the decomposition of Si2N2O into Si3N4. The elongated Si2N2O crystals contribute to the high flexural strength (161.3-228.4 MPa at room temperature) of the products. The thermal shock resistance was greatly influenced by the sample porosity, and the highest critical temperature difference (ΔTc) could be up to 1300 °C. The dielectric properties were mainly affected by the sample porosity. The as-sintered Si2N2O ceramics showed both low dielectric constant (ε<4.59) and loss tangent (tan δ<0.0049) with good mechanical properties and excellent thermal shock resistance, indicating the gas pressure sintered Si2N2O ceramics could be used as promising high temperature wave transparent material.